This invention relates to the preparation of alkali metal perfluoroalkylsulfonates by the reaction between a perfluoroalkylsulfonic acid and an inorganic alkali metal compound, and more particularly to an improved method using the same reaction for obtaining alkali metal perfluoroalkylsulfonates high in purity and very low in the concentrations of anionic impurities.
Alkali metal salts of perfluoroalkylsulfonic acids are useful as supporting electrolytes in electric cells or as catalysts for organic synthesizing reactions and polymerization reactions.
Alkali metal perfluoroalkylsulfonates are generally prepared by a neutralization reaction between a perfluoroalkylsulfonic acid and an alkali metal carbonate or hydroxide. For obtaining a high purity product by this reaction it is essential to use refined reactants. When care is taken in this regard the reaction product is very low in the concentrations of cationic impurities such as sodium, calcium, silicon, iron, lead, etc. even though the neutralization reaction is carried out in an ordinary manner and followed by simple washing and drying of the reaction product.
However, industrially refined perfluoroalkylsulfonic acids and alkali metal compounds usually contain uneligible amounts of anionic impurities such as free chlorine and free fluorine, and most of these anionic impurities remain in the product of the neutralization reaction carried out in the usual manner.
In another aspect, alkali metal perfluoroalkylsulfonates prepared by the conventional method are relatively high in moisture absorbency, and hence strict restrictions are placed on the handling of the sulfonates used for electric cells or other purposes to which moisture is detrimental.